With the progress of "aging society", the population of aged persons has recently increased and the increase in the number of senile diseases is correspondingly rapid. Among various senile diseases, dementia is of particular importance since the mechanism of its occurrence has not been fully unravelled and it can be fatal depending on its severity. Under these circumstances, the advent of an effective therapeutic agent for senile dementia is strongly desired.
Numerous studies on senile dementia have been conducted to date. The phenomena that have been reported to occur in patients with senile dementia include impairment of the central cholinergic nervous function on account of decreases in the number of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) which are enzymes that synthesize and decompose, respectively. acetylcholine known to be the transmitter of cholinergic neurons (see British Medical Journal, 2: 1457-1459, 1978; Brain, 107: 507-518, 1984; Journal of the Neurological Sciences, 57: 407-417, 1982; and Lancet, 2: 1403, 1976) and impairment of the central noradrenergic nervous function (see British Medical Journal, 282: 93-94, 1981). Researchers are making active efforts to develop drugs that are suitable for the symptomatic treatment of these phenomena.